The reason suggested for the changing shape of sexual organs may be a result of sexual conflict between males and females.

While lots of sex is good for male burying beetles wanting to pass on their genes, for the females it reduces their ability to provide parental care for offspring.

To test if sexual conflict leads to co-evolutionary changes in the shape of genitals, the researchers artificially selected pairs of burying beetles for either high mating rates or low rates for 10 generations.

The research found that this artificial selection resulted in changes in the shapes of both male and female genitalia.

It also found that changes in one sex were reflected by changes in the shape of the other sex, showing there was "co-evolution".

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Too much sex causes the male to evolve penis-like organs

Beetles selected for the higher rates of mating, where sexual conflict was higher, saw the greatest amount of genitalia shape changing, with males evolving intromittent organs and females responding by developing more pronounced claws on their genitalia.

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The reason suggested for the changing shape of sexual organs may be a result of sexual conflict

Dr Paul Hopwood added: "Although we don't know the ins and outs of how these genital structures relate to the reproductive success of each sex, our results show that sexual conflict over mating can lead to co-evolutionary changes in the shape of the genitals of burying beetles.

"Our research demonstrates the general importance of conflicts of interest between males and females in helping to generate some of the biodiversity that we see in the natural world.

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For the females it reduces their ability to provide parental care for offspring